It looks like searchify is a hosted search solution, whereas Solr and ElasticSearch are distributions of search servers that can be deployed on your own hardware.
I'm skeptical about claims of different quality of relevancy results, since IndexTank/Searchify is also based on Lucene (looks like 3.0.1 in the canonical repo), and should share all the same fundamental relevancy and scoring functionality.
It's actually heavily tweaked (this is what the IndexTank team has told me), and apparently contains components of Solr